<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <input type="text" value="123">
</body>
</html>

<script>
// 单词：temp - 临时

// 案例：如何交换两个变量的值：

var x = 123, y = 456;
var temp;

temp = x;
x = y;
y = temp;

console.log(x, y);

</script>